A number of factors are known that stimulate the growth of various cells under a variety of conditions. Most closely related to the factor disclosed herein in their activities with regard to the cells characterizing the bony and connective tissues are those which have a stimulatory effect on articular chondrocytes. These include transforming growth factor .beta. (TGF-.beta.), platelet derived growth factor (PDGF), insulin-like growth factors types I and II (IGF-I and IGF-II), acidic and basic fibroblast growth factors (FGF) and epidermal derived growth factor (EGF). (Cohen, S., et al., Adv Metab Disord (1975) 8:265-284; Froesch, E. R., et al., Ann Rev Physiol (1985) 47:443-467; Gospodarowicz, D., et al., Endocrine Reviews (1987) 8:95-114; McQuillan, D. J., et al., Biochem J (1986) 240:423-430; Ross, R., et al., Cell (1986) 46:155-169; Smith, R. L., et al., J Orthop Res (1989) 7:198-207; Tucker, R. F., et al., Cancer Res (1983) 43:1581-1586.
The known thyroid hormones, 3,3',5'-triiodo-1,3-L-thyronine (T.sub.3); thyroxine (T.sub.4) and calcitonin are known to affect connective tissue metabolism. However, their effects are generally directed to immature cells. T.sub.3 and T.sub.4 are important for growth and maturation of the epithelial cartilage secondary ossification, and generalized skeletal development; calcitonin increases hypertrophy and maturation of embryonic and growth plate cartilage, but resting cartilage is unresponsive to calcitonin.
In a recent publication, applicants disclosed the presence of an activity in partially purified thyroid calcitonin which provided stimulation of adult articular chondrocyte proliferation and glycosaminoglycan synthesis under serum-free conditions--conditions wherein none of T.sub.3, T.sub.4 or calcitonin provide such stimulation. In this paper, Jones, D. G. and Smith, R. L., J Orthoped Res (1990) 8:227-233, the disclosure of which is incorporated herein by reference, the authors disclosed that this activity could be eluted from heparin-Sepharose at low salt concentration (0.5M NaCl)--conditions under which the fibroblast growth factors, known to stimulate articular chondrocyte proliferation under similar conditions, are not eluted from this support. Acidic FGF is eluted at 1M NaCl under comparable conditions and basic FGF is eluted at 1.6M NaCl under comparable conditions (Lobb, R. R., et al., Anal Biochem (1986) 154:1-14.) The nature of this activity was not further characterized.
It has now been found that the chondrocyte stimulating activity obtainable from thyroid tissue is associated with a complex of high molecular weight components which can be prepared in isolated and purified form. The invention herein thus provides a new factor for the stimulation of connective tissue growth.